290 INDUSTRIAL PLANTS 



poppij-oil, from the seeds of tlie opium poppy (Fig. 172), and 

 nut-oil, from the kernels of the Enghsh walnut (Fig. 27 j. 

 These bi'ing comjjaratively expensive are reserved for fine 

 painting. 



Linseed-oil is invalual>le also as a .solvent for copal and 

 other resins, with which it unites at a high temperature to 

 form the highest class of varnishes. Entirely by itself it is 

 used extensively to give an attractive "oil finish" to wood- 

 work. In certain varnishes the volatile oil or spirits of tur- 

 pentine, known commonly to the trade as "turps," is the 

 solvent used, and is likewise indispensal)le to jiainters as a 

 means of thinning their colors. 



Any of the fixed oils combined with an alkali makes sonp. 

 When potash (or lye from wood ashes) is used soft soap is 

 formed; hard soap being matle with sotla. Chemically tlie 

 fixed oils are mixtures, in various proportions, of compounds 

 called glycerides. A glyceride is so called because it consists 

 of glycerin (the familiar sweetish substance soluble in water) 

 combined with an acid. Linoleic, oleic, and palmatic acids 

 are among the most im]3ortant in vegetalile oils. The gly- 

 ceride of linoleic acid, called linolein, forms SO'^f of linseed- 

 oil, and gives to this and to other drying oils their pecuhar 

 power of hardening l)y oxitlation. Olein, the glyceride of 

 oleic acid, is the main constituent of olive-oil. It is liquid 

 at ordinary temperatures and becomes rancid l)y oxidation. 

 Palmatic acid forms a glyceride, palmatin, which is not licjuid 

 at ordinary temperatures. It is tlw main s(.)lid constituent 

 of coconut and other ])alm-()ils. When any fixed oil is mixed 

 with an alkali, the glycerides present are decomposed each 

 into its peculiar acid and glycerin, and the acids unite with 

 the alkali to form soap, leaving the glycerin free. 



Inferior gratles of linseed oil and oihei- cheap oils are used 

 for soft-soa]). Oil from the olive (Fig. Ib-l) is useil extensivel>' 

 for castile, and otliei' fine toilet soa.])s. Other lia.rd soa])s of 

 various grades are matle from " coeoa-bniter " (sec secti<in o9), 

 and oils from coeontit (Fig. od), cntlon-nicd (Fig. 21.')), peonid 

 (Fig. :\2), and ohnmnl (Fig. ;'>!). 



To gi\'r an agi'reahli' (idoi' lo soap a huge X'aricly of A'olaiile 

 oils are inl rcxhiced (hu'ing llii' |)l■(l('(■^^ ol' ])rc])ariug Ihe product 



